1. Field of the Invention
This invention relates to a magnetic flux measuring device for measuring the quantity of a magnetic flux passing through a magnetic circuit.
2. Description of the Related Art
As techniques for measuring the quantity of a magnetic flux generated in a magnetic circuit, a xe2x80x9csearch coil systemxe2x80x9d, a xe2x80x9csupersaturated sensor systemxe2x80x9d, and a xe2x80x9cmagnetically sensitive element systemxe2x80x9d have been conventionally used.
In the xe2x80x9csearch coil systemxe2x80x9d, a coil is wound on a member constituting a magnetic circuit as a measuring object, and an induced electromotive force generated by the change in quantity of the magnetic flux passing through this member is detected from the coil. In the xe2x80x9csearch coil systemxe2x80x9d, the quantity of the magnetic flux in the magnetic circuit is measured by integrating the induced electromotive force generated on the coil.
In the xe2x80x9csupersaturated sensor systemxe2x80x9d, a coil is wound on a saturable magnetic material constituting a magnetic circuit as a measuring object. The coil is electrified by a driving circuit to excite the magnetic material to a magnetically saturated state. When the magnetic material is excited to a magnetically saturated state, the impedance of the coil is lowered. Moreover, if the original passing magnetic flux through the magnetic circuit is offset and added, the time of the magnetic saturation of the magnetic material changes. The longer the time of the magnetic saturation is, the lower the impedance of the coil becomes. That is, the impedance of the coil changed in accordance with the quantity of the original passing magnetic flux through the magnetic circuit. In the xe2x80x9csupersaturated sensor systemxe2x80x9d, the quantity of the magnetic flux in the magnetic circuit is measured by detecting the impedance of the coil.
In the xe2x80x9cmagnetically sensitive element systemxe2x80x9d, a gap is formed in a magnetic circuit as a measuring object and a sensor which is sensitive to magnetism such as a Hall element or an MR element is inserted into the gap, or a sensor which is sensitive to the magnetism is arranged near the magnetic circuit as a measuring object. The output of the sensor inserted or arranged in the gap or the like changes in accordance with the magnetic flux generated in the gap or the like. In the xe2x80x9cmagnetically sensitive element systemxe2x80x9d, the quantity of the magnetic flux in the magnetic circuit is measured by detecting the sensor output.
The above-described systems have the following problems.
Since the xe2x80x9csearch coil systemxe2x80x9d uses electromagnetic induction due to the magnetic flux passing through the magnetic circuit, an output can be obtained when the magnetic flux varies temporally, whereas an output cannot be obtained when the magnetic flux does not vary temporally. That is, the quantity of the unvaried magnetic flux cannot be measured. Moreover, even if the magnetic flux varies temporally, it is difficult to provide sufficient sensitivity when the quantity of temporal change is small. By increasing the number of turns of the wound coil, sufficient sensitivity may be provided even when the quantity of the temporal change is small. In such a case, however, the coil must be increased in size.
In the xe2x80x9csupersaturated sensor systemxe2x80x9d, the saturable magnetic material as the member constituting the magnetic circuit must be magnetically saturated. Therefore, if the magnetic material has, for example, a property of moderate magnetic saturation, that is, if the magnetic material requires application of a large magnetic field to be magnetically saturated (for example, electromagnetic copper plate, silicon copper plate or pure iron), a current flowing through the coil must be increased or the number of turns of the coil must be increased. This leads to increase in size of the device, deterioration in durability of the electric circuit and increase in power consumption. Moreover, even if a high permeable magnetic material which is magnetically saturated by a small magnetic field is used as the saturable magnetic material, similar problems arise when the magnetic material itself is large.
Furthermore, in the xe2x80x9csupersaturated sensor systemxe2x80x9d, a large number of magnetic fluxes which cause disturbance are generated in the magnetic circuit, other than the originally generated magnetic flux in the magnetic circuit. These magnetic fluxes might adversely affect the proper operation of the magnetic circuit itself.
In the xe2x80x9cmagnetically sensitive element systemxe2x80x9d, since the sensor is inserted in the gap in the magnetic circuit as a measuring object or arranged near the magnetic circuit, practically, a leakage flux of the magnetic circuit is detected. However, since the B-H characteristic of the magnetic material is nonlinear, the actual magnetic flux generated in the magnetic circuit is not coincident with the leakage flux, causing a measurement error.
In view of the foregoing status of the art, it is an object of the present invention to provide a magnetic flux measuring device for measuring the quantity of a magnetic flux passing through a magnetic circuit, which reduces influence on the magnetic circuit itself and realizes higher accuracy, miniaturization and lower power consumption.
In order to solve the above-described problems, the present inventor proposes the following invention.
First, a conductive core is provided on a member which forms a magnetic circuit as a measuring object. By thus providing the core on the member which forms the magnetic circuit, a magnetic flux generated in the magnetic circuit directly passes through the core. Any method for providing the core on the member may be used as long as the magnetic flux passing through the magnetic circuit directly passes through the core. For example, the member may be cut out to form a core so that a part of the member is used as the core. Alternatively, a core which is separate from the member may be inserted in the member.
Then, a coil is wound on the core and the coil is electrified at a high frequency to excite the core. The impedance of the coil at this point is detected.
The excitation of the core is carried out in consideration of the number of turns of the wound coil, the size and material of the coil, and electrical characteristics such as frequency, current and voltage of excitation driving means, and in such a manner that the core is not magnetically saturated. As the core is excited at a high frequency, the impedance of the coil includes the change in eddy current due to the conductivity of the core itself, in addition to an impedance change accompanied by self-induction. The values of these two components change with the permeability xcexc of the core material. Particularly, when the core is excited in such a manner that the core is not magnetically saturated, the impedance of the coil depends greatly on the change in eddy current. The value of the permeability xcexc of the core material changes with the quantity of the magnetic flux flowing into the core. That is, the impedance of the coil vanes with the quantity of the magnetic flux flowing into the core without magnetically saturating the core material.
According to the present invention, the impedance of the coil is detected in the above-described state and the quantity of the magnetic flux generated in the member constituting the magnetic circuit is detected on the basis of the impedance.
The above-described present invention may be realized as follows.
Specifically, a magnetic flux detecting device according to the present invention is adapted for measuring the quantity of a magnetic flux in a magnetic path forming part which forms a magnetic path and is provided within a magnetic circuit, the device comprising: magnetically sensitive means made of a conductive magnetic material and constituted by a sensor core provided on the magnetic path forming part and a sensor coil wound on the sensor core; high-frequency electrifying means for electrifying the sensor coil at a high frequency; and a magnetic flux quantity detecting means for detecting the impedance of the sensor coil and detecting the quantity of a magnetic flux in the magnetic path forming part on the basis of the impedance; the sensor core not being magnetically saturated when the sensor coil is electrified at a high frequency by the high-frequency electrifying means.
In the magnetic flux detecting device according to the present invention, a core made of a conductive magnetic material is provided on a magnetic path forming part forming a magnetic circuit. A sensor coil is wound on the core and the sensor coil is electrified at a high frequency in such a manner that the core is not magnetically saturated. The impedance of the coil is detected and the quantity of a magnetic flux in the magnetic path forming part is detected on the basis of the impedance.
Thus, the magnetic flux detecting device according to the present invention can reduce the influence on the magnetic circuit itself and can realize higher accuracy, miniaturization and lower power consumption.